The present invention relates to a method of preparing a membrane consisting of a polyantimonic acid powder and an organic binder.
Such a membrane intended for an electrochemical cell, wherein it counteracts gas diffusion and is conductive of cations in an alkaline medium or conductive of anions in an acid medium, is known from the U.S. Pat. application Ser. No. 868.800, now abandoned.
This known membrane is made by mixing polyantimonic acid powder with the binder, for instance with polytetrafluoro-ethylene, and agglomerating the powdery mixture through rolling operations.
A suchlike membrane fulfils its function of cation and anion conductor best when the weight concentration of the polyantimonic acid is fairly high, i.e. when it is ranging from 70 to 95% and preferably from 80 to 85%.
As a matter of fact, it has been found difficult in practice to prepare by this known method through rolling a membrane comprising about 80 wt % or more polyantimonic acid.
It has also been found difficult in practice to produce by this known method a membrane which is homogeneous in the whole of its thickness, being approximately 0,3 mm, and has good mechanical properties.
Finally, it has also been impossible to produce by the known process a membrane having an area which is much greater than a square decimeter.